Examination of Operator Variability for Selected Methods for Measuring Bulk Specific Gravity of Hot-Mix Asphalt Concrete

Abstract

The ability of different operators to obtain similar results when performing laboratory tests on the same material is vital for producing accurate testing results. By conducting trials in triplicate for each of three different testing methods, a measurement of the bulk specific gravity (G_mb) of compacted hot-mix asphalt concrete (HMAC) cores was obtained. An analysis of the variability between operators was investigated using a total of almost 1,300 test results, using HMAC sampled from six projects in Arkansas. Three methods were used to determine the bulk specific gravity of compacted HMAC samples, including saturated surface dry (SSD) (as per AASHTO T166), height and diameter (as per AASHTO T269), and vacuum sealing (using the Corelok vacuum sealing device). In almost all cases, G_mb values determined using the height and diameter method were statistically different from those determined using the SSD and Corelok methods; further, statistical differences were noted in paired analyses between the SSD and Corelok methods. The Corelok method exhibited a lower degree of variability than the other two methods used, based on the standard deviation of test results obtained by different operators. In direct comparison with the SSD method, the Corelok exhibited a lower variability (standard deviation) in 81 percent of the cases. Overall, the Corelok method appears to offer a viable alternative for determining the bulk specific gravity of compacted HMAC. However, agencies seeking to use the Corelok must consider the effect of an apparent shift in G_mb values obtained on resulting HMAC volumetric and compaction properties.